Liquid crystal display devices are used in applications such as clocks, calculators, various household electric appliances, measuring instruments, automotive panels, word processors, electronic organizers, printers, computers, and televisions. Typical liquid crystal display modes include the twisted nematic (TN) mode, the super-twisted nematic (STN) mode, the dynamic scattering (DS) mode, the guest-host (GH) mode, the in-plane switching (IPS) mode, the optically compensated birefringence (OCB) mode, the electrically controlled birefringence (ECB) mode, the vertical alignment (VA) mode, the color super-homeotropic (CSH) mode, and the ferroelectric liquid crystal (FLC) mode. Example addressing schemes include static addressing, multiplex addressing, simple matrix addressing, and active matrix (AM) addressing using devices such as thin-film transistors (TFTs) and thin-film diodes (TFDs).
Some display modes, including the IPS mode, the ECB mode, the VA mode, and the CSH mode, are characterized by the use of liquid crystal materials having a negative Δε. In particular, the VA display mode with AM addressing is used in applications, such as televisions, requiring high speed and wide viewing angle.
The display modes such as the VA mode require nematic liquid crystal compositions that allow for low-voltage operation, quick response, and a wide operating temperature range. Specifically, these display modes require nematic liquid crystal compositions having a negative Δε large in absolute value, low viscosity, and a high nematic phase-isotropic liquid phase transition temperature (Tni). The refractive index anisotropy (Δn) of liquid crystal materials must also be adjusted to match the cell gap (d) in terms of the product of Δn and the cell gap, i.e., Δn×d. Liquid crystal materials having a low viscosity (η) are also required for applications, such as televisions, where quick response is important.
Various compounds having a negative Δε large in absolute value have so far been researched to improve the properties of liquid crystal compositions.
As an example liquid crystal material having a negative Δε, there is disclosed a liquid crystal composition containing the following liquid crystal compounds (A) and (B) having a 2,3-difluorophenylene backbone (see PTL 1):

This liquid crystal composition contains the liquid crystal compounds (C) and (D) as compounds having a Δε of substantially zero. Unfortunately, this liquid crystal composition does not have a sufficiently low viscosity for applications, such as liquid crystal televisions, requiring quick response.

Also disclosed are liquid crystal compositions containing the compound represented by formula (E). One such liquid crystal composition contains the liquid crystal compound (D) and has a low Δn (see PTL 2). Another liquid crystal composition contains a compound, such as the liquid crystal compound (F), having an alkenyl group in the molecule thereof (i.e., an alkenyl compound), which is added to improve response speed (see PTL 3). Unfortunately, further research is needed to achieve both a high Δn and high reliability.

Also disclosed is a liquid crystal composition containing the compound represented by formula (G) (see PTL 4). Unfortunately, this liquid crystal composition contains an alkenyl compound, such as the liquid crystal compound (F), which tends to cause display defects such as burn-in and display unevenness.

The influence of liquid crystal compositions containing alkenyl compounds on display defects has been disclosed (see PTL 5). A liquid crystal composition containing a smaller amount of alkenyl compound generally has a higher η, which makes it difficult to achieve quick response. It is therefore difficult to achieve both fewer display defects and quick response.
As discussed above, it is difficult to develop a liquid crystal composition that has a negative Δε, that combines a high Δn and a low η, and that causes few or no display defects simply by the use of a compound having a negative Δε in combination with the liquid crystal compounds (C), (D), and (F).
Also disclosed is a liquid crystal composition containing the compounds of formulae (A) and (G) in combination with the compound of formula (III-F31), which has a Δε of substantially zero (see PTL 6). It is believed, however, that the amount of compound having a low vapor pressure in the liquid crystal composition cannot be increased since it evaporates at extremely low pressure during the injection of the liquid crystal composition into liquid crystal cells in the manufacture of liquid crystal display devices; therefore, the amount of compound of formula (III-F31) present in the liquid crystal composition is limited. Unfortunately, this liquid crystal composition has a high Δn but a significantly high viscosity.

PTLs 6 and 7 disclose liquid crystal compositions containing compounds having a fluorine-substituted terphenyl structure.
PTL 8 discloses the use of a liquid crystal material having a high factor as expressed by equation (1) to provide a homeotropic liquid crystal cell with improved response speed. Unfortunately, this technique is insufficient.[Math. 1]FoM=K33·Δn2/γ1  equation (1)where
K33: elastic constant
Δn: refractive index anisotropy
γ1: rotational viscosity
Accordingly, there is a need for a liquid crystal composition having a sufficiently low viscosity (η), a sufficiently low rotational viscosity (γ1), and a high elastic constant (K33) without decreased refractive index anisotropy (Δn) or nematic phase-isotropic liquid phase transition temperature (Tni) in applications, such as liquid crystal televisions, requiring quick response.